Zack Polanski has demanded the Government scrap down plans for drilling in the Rosebank oil field at a London protest.
Speaking to demonstrators outside the Department of Energy Security and Net Zero, the Green Party leader said the UK should instead "invest in our green industries".
The self-described "eco-populist" said schemes like Rosebank that make "multi-millionaires and billionaires and corporates more money" should be blocked.
The untapped oil field 80 miles west of Shetland is the UK's largest and estimated to contain up to 300 million barrels of oil.
Development was approved by the Conservative government in 2023 before being challenged following a Supreme Court ruling which said the emissions created from burning fossil fuels should be considered when granting permission for new drilling sites.
Polanski claimed at the protest that the UK is "one of the most nature depleted countries in the world".
He said: "The very least this Government need to do is to stop making things worse.
"The solutions are to invest in our green industries. The solutions are indeed in our communities to reject these huge infrastructure projects to make multi-millionaires and billionaires and corporates more money and to instead invest in our communities."
He added that his party does "not need to monger in despair and fear as (Nigel) Farage does".
Fossil Free London plan to protest outside the Department of Energy from Monday onwards until a final decision on Rosebank is made.
